The present invention relates to a diagnosing method and apparatus for sensing a non-steady state malfunction in an electric system of an electronic control system for a vehicle.
Heretofore, in diagnosing such a malfunction during the inspection of the vehicle, it has been a common practice for a mechanic to sequentially track components of the electric system based on his experience or an inspection manual in accordance with a particular condition of malfunction of the electronic control system, to diagnose the malfunction. When a number of and various types of means for electrically sensing conditions of sensing points of the vehicle are included or when a logic for controlling signals from a control unit is complex, an inspecting checker or a diagnosing apparatus called a tester has been used.
In any event, however, it is easy to diagnose the malfunction when it occurs in steady state, but since the electronic control apparatus for the vehicle is normally used in a vibrating condition, a non-steady state and non-recurrent malfunction as represented by an incomplete contact or a partial break of a wire in an electric circuit occurs frequently, and it is impossible to detect such a malfunction particularly when the malfunction occurs in a short period of time. When the electronic control system is designed for a fuel injection apparatus which electronically calculates and controls the amount of fuel injection for an engine, the malfunction in the electric system affects the safety, the ability of purifying exhaust gas and the comfortable ride and hence there is a great need for raising a probability of finding the malfunction.